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70af2f8a WL |
1 | /* |
2 | * Queue read/write lock | |
3 | * | |
4 | * This program is free software; you can redistribute it and/or modify | |
5 | * it under the terms of the GNU General Public License as published by | |
6 | * the Free Software Foundation; either version 2 of the License, or | |
7 | * (at your option) any later version. | |
8 | * | |
9 | * This program is distributed in the hope that it will be useful, | |
10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
12 | * GNU General Public License for more details. | |
13 | * | |
14 | * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P. | |
15 | * | |
16 | * Authors: Waiman Long <waiman.long@hp.com> | |
17 | */ | |
18 | #ifndef __ASM_GENERIC_QRWLOCK_H | |
19 | #define __ASM_GENERIC_QRWLOCK_H | |
20 | ||
21 | #include <linux/atomic.h> | |
22 | #include <asm/barrier.h> | |
23 | #include <asm/processor.h> | |
24 | ||
25 | #include <asm-generic/qrwlock_types.h> | |
26 | ||
27 | /* | |
2db34e8b | 28 | * Writer states & reader shift and bias. |
70af2f8a | 29 | */ |
d1331661 WD |
30 | #define _QW_WAITING 0x100 /* A writer is waiting */ |
31 | #define _QW_LOCKED 0x0ff /* A writer holds the lock */ | |
32 | #define _QW_WMASK 0x1ff /* Writer mask */ | |
33 | #define _QR_SHIFT 9 /* Reader count shift */ | |
70af2f8a WL |
34 | #define _QR_BIAS (1U << _QR_SHIFT) |
35 | ||
36 | /* | |
37 | * External function declarations | |
38 | */ | |
b519b56e | 39 | extern void queued_read_lock_slowpath(struct qrwlock *lock); |
f7d71f20 | 40 | extern void queued_write_lock_slowpath(struct qrwlock *lock); |
70af2f8a | 41 | |
70af2f8a | 42 | /** |
f7d71f20 | 43 | * queued_read_trylock - try to acquire read lock of a queue rwlock |
70af2f8a WL |
44 | * @lock : Pointer to queue rwlock structure |
45 | * Return: 1 if lock acquired, 0 if failed | |
46 | */ | |
f7d71f20 | 47 | static inline int queued_read_trylock(struct qrwlock *lock) |
70af2f8a WL |
48 | { |
49 | u32 cnts; | |
50 | ||
51 | cnts = atomic_read(&lock->cnts); | |
52 | if (likely(!(cnts & _QW_WMASK))) { | |
77e430e3 | 53 | cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts); |
70af2f8a WL |
54 | if (likely(!(cnts & _QW_WMASK))) |
55 | return 1; | |
56 | atomic_sub(_QR_BIAS, &lock->cnts); | |
57 | } | |
58 | return 0; | |
59 | } | |
60 | ||
61 | /** | |
f7d71f20 | 62 | * queued_write_trylock - try to acquire write lock of a queue rwlock |
70af2f8a WL |
63 | * @lock : Pointer to queue rwlock structure |
64 | * Return: 1 if lock acquired, 0 if failed | |
65 | */ | |
f7d71f20 | 66 | static inline int queued_write_trylock(struct qrwlock *lock) |
70af2f8a WL |
67 | { |
68 | u32 cnts; | |
69 | ||
70 | cnts = atomic_read(&lock->cnts); | |
71 | if (unlikely(cnts)) | |
72 | return 0; | |
73 | ||
77e430e3 WD |
74 | return likely(atomic_cmpxchg_acquire(&lock->cnts, |
75 | cnts, cnts | _QW_LOCKED) == cnts); | |
70af2f8a WL |
76 | } |
77 | /** | |
f7d71f20 | 78 | * queued_read_lock - acquire read lock of a queue rwlock |
70af2f8a WL |
79 | * @lock: Pointer to queue rwlock structure |
80 | */ | |
f7d71f20 | 81 | static inline void queued_read_lock(struct qrwlock *lock) |
70af2f8a WL |
82 | { |
83 | u32 cnts; | |
84 | ||
77e430e3 | 85 | cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts); |
70af2f8a WL |
86 | if (likely(!(cnts & _QW_WMASK))) |
87 | return; | |
88 | ||
89 | /* The slowpath will decrement the reader count, if necessary. */ | |
b519b56e | 90 | queued_read_lock_slowpath(lock); |
70af2f8a WL |
91 | } |
92 | ||
93 | /** | |
f7d71f20 | 94 | * queued_write_lock - acquire write lock of a queue rwlock |
70af2f8a WL |
95 | * @lock : Pointer to queue rwlock structure |
96 | */ | |
f7d71f20 | 97 | static inline void queued_write_lock(struct qrwlock *lock) |
70af2f8a WL |
98 | { |
99 | /* Optimize for the unfair lock case where the fair flag is 0. */ | |
77e430e3 | 100 | if (atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0) |
70af2f8a WL |
101 | return; |
102 | ||
f7d71f20 | 103 | queued_write_lock_slowpath(lock); |
70af2f8a WL |
104 | } |
105 | ||
106 | /** | |
f7d71f20 | 107 | * queued_read_unlock - release read lock of a queue rwlock |
70af2f8a WL |
108 | * @lock : Pointer to queue rwlock structure |
109 | */ | |
f7d71f20 | 110 | static inline void queued_read_unlock(struct qrwlock *lock) |
70af2f8a WL |
111 | { |
112 | /* | |
113 | * Atomically decrement the reader count | |
114 | */ | |
77e430e3 | 115 | (void)atomic_sub_return_release(_QR_BIAS, &lock->cnts); |
70af2f8a WL |
116 | } |
117 | ||
70af2f8a | 118 | /** |
f7d71f20 | 119 | * queued_write_unlock - release write lock of a queue rwlock |
70af2f8a WL |
120 | * @lock : Pointer to queue rwlock structure |
121 | */ | |
f7d71f20 | 122 | static inline void queued_write_unlock(struct qrwlock *lock) |
70af2f8a | 123 | { |
d1331661 | 124 | smp_store_release(&lock->wlocked, 0); |
70af2f8a | 125 | } |
70af2f8a WL |
126 | |
127 | /* | |
128 | * Remapping rwlock architecture specific functions to the corresponding | |
129 | * queue rwlock functions. | |
130 | */ | |
f7d71f20 WL |
131 | #define arch_read_lock(l) queued_read_lock(l) |
132 | #define arch_write_lock(l) queued_write_lock(l) | |
133 | #define arch_read_trylock(l) queued_read_trylock(l) | |
134 | #define arch_write_trylock(l) queued_write_trylock(l) | |
135 | #define arch_read_unlock(l) queued_read_unlock(l) | |
136 | #define arch_write_unlock(l) queued_write_unlock(l) | |
70af2f8a WL |
137 | |
138 | #endif /* __ASM_GENERIC_QRWLOCK_H */ |